Transfer hydrogenation is a general class of reactions in which hydrogen atoms from one organic molecule (donor) are used to hydrogenate another (acceptor). Many donors and acceptors have been studied. Amines have been used as donors, but not to hydrogenate nitriles. Nitriles have been used as acceptors, but not from amine donors. Nitriles have been reduced to amines with hydrogen, and amines have been dehydrogenated to nitriles and hydrogen. The present invention involves the concept of using transfer hydrogenation to equilibrate hydrogens among nitriles and amines.
Two papers by M. Besson, et al., Bull. Soc. Chim. Fr., 127, 5-12 (1990), and ibid., 13-19, describe catalytic hydrogenation of valeronitrile with Raney nickel. Their reactions were run in cyclohexane solvent with hydrogen, ammonia, and additives (pentylamine, hexylamine). They found that if the molar ratio of hexylamine/valeronitrile was greater than 0.3, hydrogenation was retarded. They also observed that hydrogen had a significant influence on the interaction of the amine with the metal surface because replacing hydrogen by nitrogen pressure gave only negligible amounts of dihexylimine and no dihexylamine was detected.
The hydrogenation of aliphatic dinitriles, NCRCN, is usually carried out to completion, i.e., with addition of 4 mol of hydrogen per mole of dinitrile, in order to prepare the corresponding diamines, H.sub.2 NCH.sub.2 RCH.sub.2 NH.sub.2. These are used, among other applications, in production of various polyamides. For example, adiponitrile is hydrogenated to hexamethylenediamine, one of the two monomers required in the production of Nylon 6,6; methylglutaronitrile is hydrogenated to methylpentamethylenediamine and/or 3-methylpiperidine; and dodecanedinitrile is hydrogenated to dodecamethylenediamine. The transfer hydrogenation process of the claimed invention is useful for the commercial production of compounds used in the production of various polyamides.